Commit 72f6fabb authored by Pierre Gondois's avatar Pierre Gondois Committed by Zeng Heng
Browse files

cpufreq: CPPC: Fix performance/frequency conversion 

mainline inclusion
from mainline-v5.18-rc1
commit ec1c7ad4
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8WAED

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ec1c7ad47664f964c1101fe555b6fde0cb124b38



--------------------------------

CPUfreq governors request CPU frequencies using information
on current CPU usage. The CPPC driver converts them to
performance requests. Frequency targets are computed as:
	target_freq = (util / cpu_capacity) * max_freq
target_freq is then clamped between [policy->min, policy->max].

The CPPC driver converts performance values to frequencies
(and vice-versa) using cppc_cpufreq_perf_to_khz() and
cppc_cpufreq_khz_to_perf(). These functions both use two different
factors depending on the range of the input value. For
cppc_cpufreq_khz_to_perf():
- (NOMINAL_PERF / NOMINAL_FREQ) or
- (LOWEST_PERF / LOWEST_FREQ)
and for cppc_cpufreq_perf_to_khz():
- (NOMINAL_FREQ / NOMINAL_PERF) or
- ((NOMINAL_PERF - LOWEST_FREQ) / (NOMINAL_PERF - LOWEST_PERF))

This means:
1- the functions are not inverse for some values:
   (perf_to_khz(khz_to_perf(x)) != x)
2- cppc_cpufreq_perf_to_khz(LOWEST_PERF) can sometimes give
   a different value from LOWEST_FREQ due to integer approximation
3- it is implied that performance and frequency are proportional
   (NOMINAL_FREQ / NOMINAL_PERF) == (LOWEST_PERF / LOWEST_FREQ)

This patch changes the conversion functions to an affine function.
This fixes the 3 points above.

Suggested-by: default avatarLukasz Luba <lukasz.luba@arm.com>
Suggested-by: default avatarMorten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: default avatarPierre Gondois <Pierre.Gondois@arm.com>
Signed-off-by: default avatarViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: default avatarZeng Heng <zengheng4@huawei.com>
parent acbbc49d

drivers/cpufreq/cppc_cpufreq.c

+23 −24
Original line number Diff line number Diff line
@@ -95,52 +95,48 @@ static u64 cppc_get_dmi_max_khz(void) 


/*

 * If CPPC lowest_freq and nominal_freq registers are exposed then we can

 * use them to convert perf to freq and vice versa

 *

 * If the perf/freq point lies between Nominal and Lowest, we can treat

 * (Low perf, Low freq) and (Nom Perf, Nom freq) as 2D co-ordinates of a line

 * and extrapolate the rest

 * For perf/freq > Nominal, we use the ratio perf:freq at Nominal for conversion

 * use them to convert perf to freq and vice versa. The conversion is

 * extrapolated as an affine function passing by the 2 points:

 *  - (Low perf, Low freq)

 *  - (Nominal perf, Nominal perf)

 */

static unsigned int cppc_cpufreq_perf_to_khz(struct cppc_cpudata *cpu_data,

					unsigned int perf)

{

	static u64 max_khz;

	struct cppc_perf_caps *caps = &cpu_data->perf_caps;

	s64 retval, offset = 0;

	static u64 max_khz;

	u64 mul, div;



	if (caps->lowest_freq && caps->nominal_freq) {

		if (perf >= caps->nominal_perf) {

			mul = caps->nominal_freq;

			div = caps->nominal_perf;

		} else {

		mul = caps->nominal_freq - caps->lowest_freq;

		div = caps->nominal_perf - caps->lowest_perf;

		}

		offset = caps->nominal_freq - div64_u64(caps->nominal_perf * mul, div);

	} else {

		if (!max_khz)

			max_khz = cppc_get_dmi_max_khz();

		mul = max_khz;

		div = caps->highest_perf;

	}

	return (u64)perf * mul / div;



	retval = offset + div64_u64(perf * mul, div);

	if (retval >= 0)

		return retval;

	return 0;

}



static unsigned int cppc_cpufreq_khz_to_perf(struct cppc_cpudata *cpu_data,

					unsigned int freq)

{

	static u64 max_khz;

	struct cppc_perf_caps *caps = &cpu_data->perf_caps;

	s64 retval, offset = 0;

	static u64 max_khz;

	u64  mul, div;



	if (caps->lowest_freq && caps->nominal_freq) {

		if (freq >= caps->nominal_freq) {

			mul = caps->nominal_perf;

			div = caps->nominal_freq;

		} else {

			mul = caps->lowest_perf;

			div = caps->lowest_freq;

		}

		mul = caps->nominal_perf - caps->lowest_perf;

		div = caps->nominal_freq - caps->lowest_freq;

		offset = caps->nominal_perf - div64_u64(caps->nominal_freq * mul, div);

	} else {

		if (!max_khz)

			max_khz = cppc_get_dmi_max_khz();
@@ -148,7 +144,10 @@ static unsigned int cppc_cpufreq_khz_to_perf(struct cppc_cpudata *cpu_data, 
		div = max_khz;

	}



	return (u64)freq * mul / div;

	retval = offset + div64_u64(freq * mul, div);

	if (retval >= 0)

		return retval;

	return 0;

}



static int cppc_cpufreq_set_target(struct cpufreq_policy *policy,